The Institute of Medicine reports that 50 to 70 million Americans suffer from what they refer to as disorders of sleep and wakefulness, including more than 30 million who suffer from sleep apnea. The current standard of care for diagnosing and monitoring these disorders is overnight polysomnography (PSG), a multiparametric test that monitors eye movement, respiratory airflow, blood oxygen saturation, hearth rhythm and other biophysical signs. Unfortunately PSG is expensive, obtrusive, and inconvenient. Patients who are already struggling with sleep are physically wired to several sensors and asked to sleep normally in a sleep lab. Also, these tests are not usually performed frequently enough to detect the night-to-night variance that many sleep disorders exhibit or to track a patient's progress after treatment has been prescribed. Based on a single night of data from a highly disruptive device, a doctor will prescribe treatment. No follow-up of the efficacy of the treatment occurs, although the patient may return to the sleep lab in 4-6 months for another evaluation.
The high cost and obtrusive nature of PSG, the gold standard for studying sleep, makes PSG an impractical tool for monitoring individuals' sleep over several nights. Other less intrusive methods have been developed to detect other movements during sleep, such as respiration. One such method has been to attach a mechanical sensor to a mat that can be placed on top of the bed (Aubert et al. 2008). The technique has high accuracy in detecting heart and respiration rates; however, the mat alters the sleeping surface of the bed and the device must be placed near the thorax of the patient.
Currently, some alternative methods for studying sleep disorders include the detection of Periodic Leg Movements (PLM), a common symptom of disruptive sleep. One popular alternative method is to use accelerometers to measure the actigraphy of leg movements. However, these devices are obtrusive and are limited in both memory and battery capacity. The KickStrip™ is a PLM monitoring device that may be placed on each leg to detect leg movements, but it is also obtrusive and merely counts the gross number of PLM's that occur within a given period of time. In contrast, the static charge sensitive bed is unobtrusive but also sensitive to all movement. As a consequence, this device cannot localize movement to the subject's legs. Portability of the device is also limited because it requires two large metal plates separated by a wood insulator.